1. Technical Field
The present invention relates to a liquid jet apparatus arranged to form predetermined characters and images by emitting microscopic droplets of liquids from a plurality of nozzles to form the microscopic particles (dots) thereof on a medium.
2. Related Art
Incidentally, in liquid jet printing apparatuses using the liquid jet apparatus, a drive signal amplified by a power amplifying circuit is applied to an actuator such as a piezoelectric element to emit a jet of a liquid from a nozzle, and if the drive signal is amplified by an analog power amplifier such as a linearly driven push-pull coupled transistor, a substantial power loss is caused, and a large heat sink for radiation is required. Therefore, according to JP-A-2005-329710, the drive signal is amplified using a digital power amplifier, thereby reducing the power loss, and eliminating the heat sink.
In the case of power-amplifying the drive signal using the digital power amplifier, it is a common practice to execute pulse modulation on a drive waveform signal acting as the basis for the drive signal, and to execute digital power amplification on the modulated signal. Incidentally, in the case of performing high-quality and high-speed printing with a one-pass operation using a line head printing apparatus, the time required for printing one dot is extremely short. For example, if a piezoelectric element is used as the actuator, it is required to pull in the liquid in the nozzle and then push it out to eject a jet within the short time required for printing a dot, and this requires a drive voltage signal with an accurate trapezoidal waveform. Since the drive waveform signal is as precise as the drive signal, in order for executing accurate pulse modulation on the precise drive waveform signal, it is required to shorten the modulation period, such as the period of a triangular wave for pulse-width modulation, or the sampling period for pulse-density modulation.
However, if the modulation period is too short, an extremely short on-duty pulse or off-duty pulse is generated at the low voltage or the high voltage in the case of, for example, the pulse-width modulation, or an extremely short on-duty or off-duty pulse is generated at an intermediate voltage in the case of, for example, the pulse-density modulation, which causes a problem that the accurate drive signal is not obtained in the case in which the switching element of the digital power amplifier does not respond to the short pulse. It is obvious that if the modulation period is made longer in order for eliminating this problem, the follow-up property to the drive waveform signal is degraded, and therefore, the accurate drive signal is not obtained after all.